Method of preventing oxidation of metals



United States Patent lVIETHOD OF PREVENTING OXIDATION OF METALS Robert A. Parson, Dyer, Ind., and. John Truhlar, Clarendon Hills, 111., assignors. to Pullman-Standard Car Manufacturing Company, Qhicago, 11]., a corporation of Delaware No Drawing. Application October 16, 1953 Serial No. 386,665

2 Claims. (Cl. I is-6.15),

The present invention relates to. the prevention of oxidation of metal surfaces, and more particularly to compositions for and a method of preventing oxidation. of such surfaces by the atmosphere.

It is an object of the invention. to provide a method of protecting metallic. surfaces. against oxidation by the atmosphere to prevent corrosion. thereof.

Another object is the provision. of a method of shield ing a metallic surface against oxidation by the atmosphere by forming a film thereon.

Another object is the provision of amethod of doubly shielding a ferrous metal surface against rusting by forming, a film thereon and an alkaline atmosphere adjacent thereto.

Another object is the provision of. compositions which may be applied to metallic surfaces toprevent. oxidation thereof by the atmosphere.

Another object is the provision of compositions which may be applied to metallic surfaces to. form protective films thereon preventing oxidation thereof.

Another object is the provision of compositions form.- ing a protective film on and. an. alkaline atmosphere about metal surfaces to prevent. oxidation thereof.

These and other objects of the invention are achieved by the utilization of certain phosphates set forth hereinafter which have been found to have an oxidation-preventiing action on metals. The invention provides a method and compositions employing such phosphates for. preventing oxidation of metals, as now described.

Such phosphates when properly employed prevent.

metal oxidation for substantial periods, the di-ammonium phosphate having a double action which is particularly advantageous in certain applications. The invention appears at present to have its greatest usefulness in the prevention of rusting of ferrous metals and alloys, but

is not limited in its application to any particular class or type of metals and is of value wherever rust, corrosion, or other effects on metal due to oxidation present aproblem, and is of great importance in the cases of certain metals, such' as aluminum for example-, in which oxidation is particularly undesirable.

The method of this invention comprises essentially the application of a phosphate to the surface of a metal part, article, or object which it is desired to protect against oxidation, This maybe accomplished in any suitable manner, as by laving, immersing, brushing, spraying, or dusting the object with ,or in a composition, liquid or solid, containing the phosphate, so as; to subject. the. surface or surfaces thereof to the action of the phosphate. Of course, the article or object should have its surface substantially clean and uncorroded at the time of ap plication of the phosphate in order to obtain the best results. After the application, the object may be left ex posed to the atmosphere for a long period, a matter of days or weeks, without harm to the treated surfaces due to oxidation, so that a subsequent operation on the surfaces need not be performed immediately and may follow the application of the phosphate after a considerable lapse of time without complications or preliminary operations caused or required by corrosive or like effects resulting from, oxidation. Inmany if not most cases, the application of the phosphate may conveniently be combined with another operation required to be performed on the object. Thus, for example, the phosphate may be applied during amachining operation on the article by employing: as themachining coolant a liquid composition including. a desired proportion of the phosphate together with, say; a cutting oil and water, and flowing the coolant over the object during the machining operation in the usual manner.

Compositions incorporating the phosphate may be of any suitable or convenient type, such as solutions, suspensions, emulsions, mixtures, or the like, or in the form of paints, varnishes, lacquers, or like coating materials, all of. which are hereinafter designated generally as dispersions, which term employed in a broad sense as including liquid, solid, or intermediate compositions in which the phosphate is dispersed or intermingled, whether it be dissolved, suspended, or otherwise mixed therein. Thus the composition may be a solution of a desired proportion of the phosphate in a suitable solvent, or a dry powder comprising an appropriate inert material with the phosphate in powdered form mixed therewith, to give only two possible examples. Thematerial in which the phosphate is dispersed serves as a vehicle or medium for the phosphate, but it may alsohave some other function, as in the case of the machining coolant mentioned above. It is not. necessary that the phosphate be combined with some other material, and it may be employed alone if desired and not in a composition or dispersion, but because only relatively small quantities of the phosphate are required for' effective results it is ordinarily more convenient and economical to employ a composition in which the phosphate is included in a desired proportion. One important. type of composition employing the invention is represented by the coolant mentioned hereinabove as an example, which may typically comprise an emulsion ofoil and water witha'small proportion' of the phosphate dispersed therein. The oil and water emulsion if employed alone: as a. coolant in a machining operation will: not prevent. formation of rust on a ferrous article. during the interim between the machining operation andsubsequent machining or other operations, but if it is employed in a compositionas a medium for the. phosphate while also functioning as a coolant and lubricant, rusting of. the article is prevented for a desired. period: sufficient to allow of. such subsequent operations being. performed after a delay ofdays or weeks without complications. Of course, the same is true-v in connection: with: undesired sheets of oxidation of non-ferrous metals.

The amount. of. phosphate required to prevent oxidation varies in. different cases, depending upon such factors as the length of time for which protection is desired, the severity of the condition. to which the article or object is subjected, the manner of. application to the In general, only a metal, and similar considerations. relatively small amount isnecessary. As little as 0.01% by weight, or even less, in an. appropriate vehicleor medium may beqsufiicientn under some circumstances, and the proportion may increase almost indefinitely, at least theoretically, although in practice considerations of economy, coupled with the fact that beyond a certain point increase in the amount or proportion of phosphate does not result in additional protection, would ordinarily dictate'the minimum. It has been found that generally a proportion of the phosphate between 0.5% and 3% is sufficient for excellent results in protecting ferrous articles against rust for periods of several days to weeks, and similarly in preventing oxidation of other metals,

3. In most cases, a proportion of 1% to 2% will achieve the desired results. The phosphate is employed in a proportion of 2% in the oil and water machining coolant described hereinabove used on articles of ferrous metal or alloys to obtain the results stated. Due to the multiplicity and diversity of the possible applications of the invention, no single, hard-and-fast rule can be laid down as to the quantity of phosphate to be employed in all cases.

Because of its cheapness and availability and lack of deleterious effects on ferrous metals and alloys, which because of their widespread use and subjection to rusting afford a major field for the application of the present invention, as well as on many other metals, di-ammonium phosphate is preferred, in general, in all cases where it will not deleteriously afiect the metal. Diammonium hydrogen orthophosphate is considered especially desirable because it is the cheapest and yet gives excellent results. 9

Another factor tending to the preference of the diammonium phosphate lies in a double protective action which it provides. Phosphates of the defined class or group decompose slowly at ordinary temperatures, which is one reason for the long periods of oxidation prevention they afford. The phosphate radical reacts with the metal to form a film of a salt of the metal on the surface, thus preventing exposure of the surface to the oxygen of the atmosphere and avoiding the effects of oxidation of the metal surface. The di-ammonium phosphate in addition to this protection provides an alkaline atmosphere on or adjacent the metal surface in the form of ammonia gas evolved from the ammonium radical. While this gaseous ammonia atmosphere is quickly dissipated from the exterior surfaces of objects treated with this phosphate, it is at least largely retained within hollow articles or objects and provides a protective blanket for the interior surfaces to shield them against oxidation. Such interior surfaces are thus doubly protected, by the film produced by the reaction of the phosphate radical and by the alkaline atmosphere produced by the ammonium radical. In the case of hollow articles of metal unharmed by ammonia, therefore, the use of diammonium phosphate has an additional advantage.

A few examples of the results obtained by the use of diammonium hydrogen orthophosphate to prevent corrosion of steel and other ferrous metal objects will serve to illustrate the practical advantages of the invention. Finished machined objects of ferrous metals often begin to rust within a matter of minutes under certain conditions, and cleaning or other solutions containing corrosive substances tend to rust and pit such objects, as is well known. As one instance, bodies requiring various machining operations rusted in the interim between such operations. The use of a composition of about 2% diammonium hydrogen orthophosphate dispersed in a water and oil emulsion and used as a coolant in the machining operations prevented corrosion not only for the normal periods between such operations but for at least several days and permitted painting of the bodies even at the end of such periods without difficulty due to corrosion. In another case, steel parts cleaned by vapor degreasing corroded very rapidly when handled for inspection, the corrosion being accelerated by exposure to acid fumes from a soldering operation, and preservative oils had no appreciable effect in retarding cleanliness.

rusting. By dipping the parts in a 2% aqueous solution of diammonium hydrogen orthophosphate for a period of from several seconds to a few minutes, rusting is prevented for many days. Again, steels subjected to metal cleaners, especially those of the acid type, as by immersion or by exposure at intervals, become pitted and are generally attacked by such cleaners, as for example steel used as the outer sheathing of railway passenger cars subjected to periodic washing. The use of only a small proportion of the diammonium acid orthophosphate, of the order of 2% in such cleaners, prevents initial attack of the steels by the cleaners and thus minimizes the possibility of corrosion due to the elements. The invention is applicable to many situations in which oxidation of metal has not been satisfactorily controllable. Steel sheets at present are generally coated with a preservative oil to prevent corrosion in shipment and storage, but this procedure is largely ineffective in accomplishing its intended purpose, and in addition causes dirt accumulation and creates difficulties in handling of the sheets. The present invention provides cheaper, more effective protection against corrosion of steel sheets than the use of oil and raises no problems as to handling or The protection of basic steel products thus represents one important field for application of the invention, and many others in addition to those already pointed out might be mentioned.

It will be apparent that the invention in its several aspects provides a ready, economical solution to the problems resulting from oxidation of metals, and effects a great savingin the time, labor, and equipment investment now required to prevent or remove the effects of oxidation, as well as simplifying manufacturing operations.

What is claimed is:

l. A method of preventing oxidation of the interior surface of a hollow ferrous metal article which comprises subjecting said surface to the action of di-ammonium phosphate to form on the surface a film of a salt of the metal by reaction of the phosphate radical therewith and produce adjacent the surface a gaseous ammonia atmosphere evolved from the ammonium radical.

2. A method of preventing atmospheric oxidation of the surface of an article of metal unaffected by ammonia which comprises subjecting said surface to the actionof di-ammonium phosphate to form on the surface a film of a salt of the metal by reaction of the phosphate radical therewith and produce adjacent the surface a gaseous ammonia atmosphere evolved from the ammonium radical whereby to shield the surface against oxidation by atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 1,428,087 Gravell Sept. 5, 1932 2,008,939 Tufts July 23, 1935 2,252,385 Orozco Aug. 12, 1941 2,258,309 Zimmer Oct. 7, 1941 2,285,855 Downing et al June 9, 1942 2,328,540 Hochwalt Sept. 7, 1943 2,430,400 Hoelscher Nov. 4, 1947 2,439,927 Haas Apr. 20, 1948 2,515,590 Swain et al. June 20, 1950 2,552,874 Snyder et al. May 15, 1951 2,665,995 Bishop Jan. 12, 1954 

1. A METHOD OF PREVENTING OXIDATION OF THE INTERIOR SURFACE OF A HOLLOW FERROUS METAL ARTICLE WHICH COMPRISES SUBJECTING SAID SURFACE TO THE ACTION OF DI-AMMONIUM PHOSPHATE TO FORM ON THE SURFACE A FILM OF A SALT OF THE METAL BY REACTION OF THE PHOSPHATE RADICAL THEREWITH AND PRODUCE ADJACENT THE SURFACE A GASEOUS AMMONIA ATMOSPHERE EVOLVED FROM THE AMMONIUM RADICAL. 